In the past, several attempts had been performed for coupling a low molecular chemical drug with a high molecule, in order to give desirable distribution of the drug in the body so as to increase a drug half-life in the body. However, high-molecular compounds used in these attempts were copolymers consisting of one component, or polymers in which two components were polymerized alternatively or randomly.
In the cases of polymers above described when amounts of carried drugs increase for improvement of their efficacy, their water-solubility decreases owing to the hydrophobic nature of the drugs. The task of the present invention is to provide a water-soluble drug which does not decrease its water-solubility even if amounts of carried drugs were increased.
The present inventors tried to develop a high molecular polymerized drug, in order to solve the problem of the conventional high molecular polymerized drug. As a result of their eager research, they introduced a drug selectively to a second segment of a block copolymer comprising a first segment and the second segment, to give it hydrophobic nature. They succeeded in preventing the decrease of water-solubility accompanied by introduction of a drug and in preventing precipitate formation, by means of micelle formation in which the second segment is the inner-core and the first segment the outer-shell. The high molecular polymerized drug developed by the present inventors possesses good water-solubility, as well as attains, as a drug, stability in an aqueous solution higher than its original drug by use of the micelle formation.